Multiple Tube Bank Flattened Tube Finned Heat Exchanger

ABSTRACT

A multiple tube bank heat exchanger includes a first tube bank ( 100 ) including at least a first and a second flattened tube segments extending longitudinally in spaced parallel relationship and a second tube bank ( 200 ) including at least a first and a second flattened tube segments extending longitudinally in spaced parallel relationship. The second tube bank ( 200 ) is disposed behind the first tube bank ( 100 ) with a leading edge of the second tube bank spaced from a trailing edge of the first tube bank. A continuous folded plate fin extends between the first and second flattened tube segments of both of said first tube bank and said second tube bank.

CROSS-REFERENCE TO RELATED APPLICATION

Reference is made to and this application claims priority from and thebenefit of U.S. Provisional Application Ser. No. 61/416,145, filed Nov.22, 2010, entitled “Multiple Tube Bank Flattened Tube Finned HeatExchanger”, which application is incorporated herein in its entirety byreference.

FIELD OF THE INVENTION

This invention relates generally to heat exchangers and, moreparticularly, to flattened tube and fin heat exchangers.

BACKGROUND OF THE INVENTION

Heat exchangers have long been used as evaporators and condensers inheating, ventilating, air conditioning and refrigeration (HVACR)applications. Historically, these heat exchangers have been round tubeand plate fin (RTPF) heat exchangers. However, flattened tube plate finheat exchangers are finding increasingly wider use in industry,including the HVACR industry, due to their compactness, structuralrigidity, lower weight and reduced refrigerant charge requirement, incomparison to conventional RTPF heat exchangers.

A typical flattened tube plate fin heat exchanger includes a firstmanifold, a second manifold, and a single tube bank formed of aplurality of longitudinally extending flattened heat exchange tubesdisposed in spaced parallel relationship and extending between the firstmanifold and the second manifold. Additionally, a plurality of platefins are disposed between each neighboring pair of heat exchange tubesfor increasing heat transfer between a fluid, commonly air in HVACRapplications, flowing over the outer surface of the flattened tubes andalong the fin surfaces and a fluid, commonly refrigerant in HVACRapplications, flowing inside the flattened tubes. In an embodiment offlattened tube commonly used in HVACR applications, termedmulti-channel, mini-channel or micro-channel tubes, the interior of theflattened tube is subdivided into a plurality of parallel flow channels.For example, U.S. Pat. No. 6,964,296 shows a flattened tube flat platefin heat exchanger in both a single tube bank and a double tube bankembodiment with horizontal tube runs and vertically extending flat platefins.

A concern associated with the use of flattened tube heat exchangers inHVACR applications is poor drainage of condensate/water from the surfaceof the flattened tubes. The retention of condensate/water can beparticularly problematic in flattened tube heat exchangers havinghorizontal tubes with high fin density and close tube spacing. In suchconstructions, condensate/water tends to collect on the flat horizontalsurfaces of the heat exchange tubes in the spaces between the denselypacked fins. The condensate/water collecting on the external surfaces ofthe heat exchanger tubes acts as an electrolyte and tends to acceleratecorrosion and pitting of the tube surface. Condensate/water retention onthe horizontal surface of the heat exchanger tube may also result inincreased airside pressure drop and reduced air flow, as well as causean undesirable condensate blow-off effect. Any condensate/watercollecting on the horizontal tube surface also constitutes a layer ofadded thermal resistance to heat transfer on the airside of the heatexchange tubes.

Accordingly, the need exists for a flattened tube finned heat exchangerthat is substantially free draining of condensate/water off thehorizontal flat surface of the flattened horizontally extendingflattened heat exchange tubes. The desire also exists for a flattenedtube finned heat exchanger that is substantially free draining ofcondensate/water, while also achieving enhanced thermal performance.

SUMMARY OF THE INVENTION

In an aspect, a heat exchanger includes a first tube bank including atleast a first and a second flattened tube segments extendinglongitudinally in spaced parallel relationship, a second tube bankincluding at least a first and a second flattened tube segmentsextending longitudinally in spaced parallel relationship, the secondtube bank disposed behind the first tube bank with a leading edge of thesecond tube bank spaced from a trailing edge of the first tube bank, anda continuous folded fin plate extending between the first and secondflattened tube segments of both of the first tube bank and the secondtube bank. The continuous folded fin plate may comprise a louvered platehaving a first louvered section extending between the first and secondflattened tube segments of the first tube bank and a second louveredsection extending between the first and second flattened tube segmentsof the second tube bank. The continuous folded plate fin may furthercomprise a transition section between the first louvered section and thesecond louvered section, the transition section positioned between atrailing edge of the first tube bank and a leading edge of the secondtube bank. The louvers of the first louvered section are oriented at aforward angle and the louvers of the second louvered section areoriented at a back angle. The transition section may include condensatedrainage notches.

In an aspect, a heat exchanger is provided for passing a refrigerant inheat exchange relationship with an air flow passing through an air sideof the heat exchanger. The heat exchanger includes a first tube bankincluding a plurality of flattened tube segments extendinglongitudinally in spaced parallel relationship, and a second tube bankincluding a plurality of flattened tube segments extendinglongitudinally in spaced parallel relationship, said second tube bankdisposed downstream with respect to the first tube bank with a leadingedge of the second tube bank spaced from a trailing edge of the firsttube bank, wherein the air flow passes first transversely across theflattened tube segments of the first tube bank and then passestransversely across the flattened tube segments of the second tube bank,and the refrigerant flows first through the flattened heat exchange tubesegments of the second tube bank and then through the flattened heatexchange tube segments of the first tube bank. In an embodiment, theheat exchange tube segments of the second tube bank are arranged in anin-line arrangement with the heat exchange tube segments of the firsttube bank. In an embodiment, the heat exchange tube segments of thesecond tube bank are arranged in a staggered arrangement with the heatexchange tube segments of the first tube bank.

In an aspect, a parallel-counterflow heat exchanger is provided forpassing a refrigerant in heat exchange relationship with an air flowpassing through an air side of the heat exchanger. The heat exchangerincludes at least a first tube bank and a second tube bank, each of saidtube banks having a first pass including a first plurality of flattenedheat exchange tube segments extending longitudinally in spaced parallelrelationship and a second pass including a second plurality of flattenedheat exchange tube segments extending longitudinally in spaced parallelrelationship. The air flow passes first transversely across theflattened tube segments of said first tube bank, and passes secondtransversely across the flattened tube segments of said second tubebank. The refrigerant flows first through the first pass of the firsttube bank, then through the first pass of the second tube bank, thenthrough the second pass of the second tube bank, and then through thesecond pass of the first tube bank. In an embodiment, well adapted foruse as an evaporator, the first plurality of heat exchange tube segmentsof the first pass of the first tube bank collectively define a firstrefrigerant flow area, the first plurality of heat exchange tubesegments of the first pass of the second tube bank collectively define asecond refrigerant flow area; the second plurality of heat exchange tubesegments of the second pass of the second tube bank collectively definea third refrigerant flow area, and the second plurality of heat exchangetube segments of the second pass of the first tube bank collectivelydefine a fourth refrigerant flow area. The respective refrigerant flowareas becoming progressively larger from the first refrigerant flow areato the second refrigerant flow area to the third refrigerant flow areato the fourth refrigerant flow area.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the disclosure, reference will be made tothe following detailed description which is to be read in connectionwith the accompanying drawing, where:

FIG. 1 is a diagrammatic illustration of an exemplary embodiment of amultiple tube bank, flattened tube finned heat exchanger as disclosedherein;

FIG. 1A is a side elevation cut out illustrating the fin and tubearrangement of the flattened tube finned heat exchanger of FIG. 1;

FIG. 2 is a sectioned plan view of a portion of an exemplary embodimentof a multiple tube bank, flattened tube finned heat exchanger takengenerally along line 2-2 of FIG. 1;

FIG. 3 is a sectioned side elevation view of the embodiment of themultiple tube bank, flattened tube finned heat exchanger of FIG. 2;

FIG. 4 is a sectioned side elevation view of an alternate embodiment ofthe multiple tube bank, flattened tube finned heat exchanger of FIG. 3;

FIG. 5 is a perspective view of a single fold of the continuous foldedfin plate of the heat exchanger disclosed herein;

FIG. 6 is a section plan view through the fins of the single fold of thefolded fin plate shown in FIG. 5;

FIG. 7 is a diagrammatic view of the multiple tube bank heat exchangerdisclosed herein illustrating an exemplary cross-counterflow refrigerantcircuit;

FIG. 8 is a diagrammatic view of the multiple tube bank heat exchangerdisclosed herein illustrating another exemplary cross-counterflowrefrigerant circuit;

FIG. 9 is a diagrammatic view of the multiple tube bank heat exchangerdisclosed herein illustrating another exemplary cross-counterflowrefrigerant circuit;

FIG. 10 is a diagrammatic view of the multiple tube bank heat exchangerdisclosed herein illustrating another exemplary cross-counterflowrefrigerant circuit;

FIG. 11 is a diagrammatic view of the multiple tube bank heat exchangerdisclosed herein illustrating another exemplary cross-counterflowrefrigerant circuit;

FIG. 12 is a diagrammatic view of the multiple tube bank heat exchangerdisclosed herein illustrating another exemplary cross-counterflowrefrigerant circuit;

FIG. 13 is a diagrammatic view of a multiple tube bank heat exchangerdisclosed herein illustrating a parallel-counterflow refrigerantcircuit; and

FIG. 14 is a sectioned side elevation view of an exemplary embodiment ofa multiple tube bank flattened tube finned heat exchanger showing afirst and a second tube bank arranged in a staggered heat exchange tubearrangement.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIGS. 1 and 2 of the drawing, there is depictedan exemplary embodiment of a multiple bank flattened tube finned heatexchanger 10 in accordance with the disclosure. As depicted therein, theheat exchanger includes a first tube bank 100 and at least a second tubebank 200 that is disposed behind the first tube bank 100. Each of thefirst tube bank 100 and the second tube bank 200 includes a firstmanifold 102, 202 extending along a vertical axis and a second manifold104, 204 also extending along a vertical axis. It is to be understoodthat the multiple bank flatted tube finned heat exchanger 10 disclosedherein may include more than two tube banks.

The first manifold 102 and the second manifold 104 of the first tubebank 100 are spaced apart from one another with a plurality of heatexchange tube segments 106, that is at least a first and a second tubesegment, extending longitudinally in spaced parallel relationshipbetween and connecting the first manifold 102 and the second manifold104 in fluid communication. Similarly, the first manifold 202 and thesecond manifold 204 of the second tube bank 200 are spaced apart fromone another with a plurality of heat exchange tube segments 206, that isat least a first and a second tube segment, extending longitudinally inspaced parallel relationship between and connecting the first manifold202 and the second manifold 204 in fluid communication. The neighboringmanifolds at the ends of the tube banks 100, 200 may be separatemanifolds, such as depicted in FIG. 2 with respect to first manifold 102and first manifold 202, connected by appropriate piping as necessary toaccommodate the particular refrigerant circuitry incorporated into theheat exchanger 10, or the neighboring manifolds at the ends of the tubebanks 100, 200 may be combined or integrated into a single manifold,such as depicted in FIG. 2 with respect to second manifold 104 andsecond manifold 204, subdivided into chambers as appropriate, whichchambers are fluidly interconnected internally within the singlemanifold as necessary to accommodate the particular refrigerantcircuitry incorporated into the heat exchanger 10.

Each of the heat exchange tube segments 106, 206 comprises a flattenedheat exchange tube having a leading edge 108, 208, a trailing edge 110,210, an upper flat surface 112, 212, and a lower flat surface 114, 214.The interior of each of the heat exchange tube segments 106, 206 may bedivided by longitudinally extending interior walls into a plurality ofparallel flow channels 120, 220 that establish fluid communicationbetween the respective headers of the first and the second tube banks100, 200. The second tube bank 200 is disposed behind the first tubebank 100, with respect to the airflow direction, with the leading edge208 of the second tube bank 200 spaced from the trailing edge 110 of thefirst tube bank 100 by a relatively narrow gap, G, of about 2 to 4millimeters (mm) (0.08 to 0.15 inches). In the depicted embodiment, eachof the heat exchange tube segments 106, 206 of the first and second tubebanks 100, 200, respectively, comprises a multi-channel tube having aninterior flow passage divided by interior walls into a plurality ofdiscrete flow channels 120, 220 that extend longitudinally the length ofthe tube from an inlet end of the tube to the outlet end of the tube.However, it is to be understood that the tube banks 100, 200 couldinclude serpentine tubes with the heat exchange tube segments 106, 206being parallel linear tube segments connected by U-bends or hairpinturns to form a serpentine tube connected at its respective ends betweenthe first manifold and the second manifold of the tube bank.

The flattened tube finned heat exchanger 10 disclosed herein furtherincludes a plurality of folded fin plates 20. Each folded fin plate 20is formed of a single continuous plate of fin material tightly folded ina ribbon-like fashion thereby providing a plurality of closely spacedfins 22 that extend generally orthogonal to the flattened heat exchangetubes 106, 206. Typically, the fin density of the closely spaced fins 22of each continuous folded fin plate 20 may be about 18 to 25 fins perinch, but higher or lower fin densities may also be used. The depth ofeach of the ribbon-like folded plate 20 extends from the leading edge108 of the first tube bank 100 to the trailing edge of 210 of the secondbank 200 and spans the gap, G, between the trailing edge 110 of thefirst tube bank 100 and the leading edge 208 of the second tube bank200. In an embodiment of the heat exchanger 10, the manifolds, heatexchange tubes and fins are all made of aluminum or aluminum alloymaterial.

Referring now to FIGS. 5 and 6, a single fold of the continuousribbon-like folded fin plate 20 is depicted and shows two fins 22. Eachfin 22 has a first section 24, a second section 26 and a third section28. When installed in the heat exchanger 10, the first section 24 isdisposed within the first tube bank 100, the third section 28 isdisposed within the second tube bank 200, and the second section 26spans the gap, G, between the trailing edge 110 of the first tube bank100 and the leading edge 208 of the second tube bank 200. The first andsecond sections 24 and 28 may be provided with louvers 30, 32 formed ina conventional manner in the material of the fin plate 20. In thedepicted embodiment, the louvers 30 formed in the first section 24 areforward angled relative to the direction (indicated by the arrow in FIG.6) of flow along the fins 22 and the louvers 32 formed in the thirdsection 28 are back angled relative to the direction of flow along thefins 22. In the depicted embodiment, both the louvers 30 in both firstsection 24 and louvers 32 in the third section 28 of each fin 22 areforward and back angled, respectively, at a desired louver angle, A. Thesecond section 26 comprises a turn-around louver 34 that provides atransition between the forward angled louvers 30 of the first section 24and the back angled louvers 32 of the third section 28 of each fin 22.When installed in the heat exchanger 10, the second section 26 spanningthe gap, G, between the first tube bank 100 and the second tube bank 200provides a drainage path for condensate/water collecting on thehorizontally disposed upper flat surfaces 114, 214 of the flattened heatexchange tube segments 106, 206.

In the embodiment of the heat exchanger 10 depicted in FIG. 3, the firsttube bank 100 and the second tube bank 200 have the same number of heatexchange tube segments 106, 206 extending longitudinally andhorizontally in spaced parallel relationship between their respectivemanifolds at the same tube spacing. Additionally, the heat exchange tubesegments 206 are disposed in direct alignment with the heat exchangetube segments 106. In this arrangement, a continuous folded plate fin 20is disposed between each pair of adjacent aligned sets of tube segments106, 206.

However, the first tube bank 100 and the second tube bank 200 need nothave the same number of heat exchange tube segments 106, 206. Rather,the number of heat exchange tubes 106 in the first tube bank 100 mayhave a different number of heat exchange tubes 206 in the second tubebank 200. For example, in the embodiment of the heat exchanger 10depicted in FIG. 4, every other heat exchange tube 106 in the first tubebank 100 has been removed such that the first tube bank 100 has a lowernumber of heat exchange tube segments 106 than the number of heatexchange tube segments 206 of the second tube bank 200. In thisparticular embodiment, every other tube segment 206 of the second tubebank 200 is directly aligned behind a tube segment 106 of the first tubebank 100, while the remaining tube segments 206 do not have acorresponding tube segment 106 disposed upstream thereof.

It should be noted that in embodiments wherein the first and second tubebanks 100, 200 have an unequal number of tube segments 106, 206, aplurality of continuous folded fin plates 20 may extend through bothtube banks with the number of continuous fin plates 20 determined suchthat a continuous fin plate 20 is disposed between each pair of adjacentheat exchange tube segments of the tube bank having the greater numberof heat exchange tube segments 106, 206. However, alternatively, some ofthe fin sections in the tube bank having the lower number of heatexchange tube segments may be removed so that some of the folded finplates, but not all, extend only from the leading edge to the trailingedge of the tube bank having the greater number of heat exchange tubesegments.

The tube width may also be different between the heat exchange tubesegments 106 positioned in the first tube bank 100 and the heat exchangetube segments 206 positioned in the second tube bank 200. In general,the widths of the heat exchange tube segments 106, 206 of the multiplebank heat exchanger 10 would typically range from 12 to 32 mm (about 0.5to 1.5 inch). Since the number of flow channels 120, 220 within theflattened heat exchange tube segments 106, 206, respectively, typicallyvaries directly with tube width, the number of flow channels 120, 220 ineach of the heat exchange tube segments 106, 206, respectively, may bedifferent and be tailored to the refrigerant thermo-physical properties,such as density.

For instance, for condenser heat exchangers in air conditioning orrefrigeration applications, the heat exchange tubes of the downstreamtube bank with respect to the refrigerant flow, which in the embodimentdepicted in FIGS. 1 and 3, would be the first tube bank 100, would havelower width tube segments 106, as compared to the width of the heatexchange tube segments 206 of the second tube bank 206, i.e. theupstream tube bank with respect to refrigerant flow, to accommodate therefrigerant condensing process and maintain desired refrigerant flowvelocity in the channels of the heat exchange tube segments in thedownstream tube bank for the appropriate balance between heat transferand pressure drop characteristics.

Reducing the number of heat exchange tube segments in the downstreamtube bank with respect to refrigerant flow, whether or not inconjunction with reducing the width of the heat exchange tube segmentsin the downstream tube bank, relative to the number of heat exchangetube segments in the upstream tube bank with respect to refrigerantflow, is also effective in accommodating the refrigerant condensingprocess and maintaining desired refrigerant flow velocity in the flowchannels of the heat exchange tube segments in the downstream tube bankfor the appropriate balance between heat transfer and pressure dropcharacteristics. Additionally, the cross-sectional flow area through theheat exchange tube segments of the downstream tube bank with respect torefrigerant flow may reduced by decreasing the cross-sectional flow areaof the multiple flow channels or decreasing the number of the flowchannels to accommodate the condensing refrigerant flow, whilemaintaining outside geometrical characteristics identical to those ofthe upstream tube bank with respect to refrigerant flow.

These concepts can be applied to evaporator heat exchangers in airconditioning or refrigeration applications in the reversed manner. Forexample, for evaporator heat exchangers, the heat exchange tubes of theupstream tube bank with respect to the refrigerant flow could have lowerwidth tube segments as compared to the width of the heat exchange tubesegments of the downstream tube bank with respect to refrigerant flow.

In conjunction with multiple tube banks having different width heatexchange tube segments, the louvered fins 22 of the continuous foldedfin plates 20 may be asymmetrical with the first section 24 and thethird section 28 sized differently to match the respective tube widthsof the first and second tube banks 100, 200. If the heat exchange tubesegments 106, 206 have the same tube width, then the fins 22 are withthe first and third fin sections 24, 28 being of equal length and thesecond sections 26, i.e. the turn-around louver section, of the fins 22being centrally located between the first and third sections 24, 28.However, for a heat exchanger configuration having tube banks ofdissimilar tube width, the second section 26, i.e. the turn-aroundlouver section, is not positioned centrally in the fin 22, but rather islocated off-center in the fin between the first section 24 and the thirdsection 28 of the fin.

Nevertheless, the second section 26, i.e. the turn-around louversection, should again be aligned to span the gap, G, between thetrailing edge of the first tube bank 100 and the leading edge of thesecond tube bank 200, such as illustrated in FIGS. 3 and 4, becausealigning the turn-around louver sections 26 of the louvered fins 22 withthe gap, G, between the tube banks provides improved condensate/waterdrainage from the surface of the flattened heat exchange tube segments.Designs with presence of notches at the turn-around louver willnecessitate use of asymmetrical louver bank.

Referring now again to FIG. 1, the multiple tube bank flattened tubefinned heat exchanger 10 will be described as configured as a condenserheat exchanger in a refrigerant vapor compression system of an airconditioning unit, transport refrigeration unit or commercialrefrigeration unit. In such applications, refrigerant vapor from thecompressor (not shown) of the refrigerant vapor compression system (notshown) passes through the manifolds and heat exchange tube segments ofthe tube banks 100, 200, in a manner to be described in further detailhereinafter, in heat exchange relationship with a cooling media, mostcommonly ambient air, flowing through the airside of the heat exchanger10 in the direction indicated by the arrow labeled “A” that passes overthe outside surfaces of the heat exchange tube segments 106, 206 and thesurfaces of the folded fin plates 20.

The multiple tube bank flattened tube finned heat exchanger 10 depictedin FIG. 1 has a cross-counterflow circuit arrangement. The air flowfirst passes transversely across the upper and lower horizontal surfaces112, 114 of the heat exchange tube segments 106 of the first tube bankand then passes transversely across the upper and lower horizontalsurfaces 212, 214 of the heat exchange tube segments 206 of the secondtube bank 200. The refrigerant passes in cross-counterflow arrangementto the airflow, in that the refrigerant flow passes first through thesecond tube bank 200 and then through the first tube bank 100. In theprocess, the refrigerant passing through the flow channels of the heatexchange tubes 106, 206 rejection heat into the airflow passing throughthe air side of the heat exchanger 10. The multiple tube bank flattenedtube finned heat exchanger 10 having a cross-counterflow circuitarrangement yields superior performance, as compared to the crossflow orcross-parallel flow circuit arrangements.

More specifically, in the embodiment depicted in FIG. 1, the refrigerantflow, designated by the label “R”, passes from the refrigerant circuit(not shown) into the first manifold 202 of the second tube bank 200 andis distributed amongst the heat exchange tube segments 206 to flowtherethrough into the second manifold 204 of the second tube bank 200.The refrigerant collecting in the second manifold 204 of the second tubebank 200 then passes into a lower section 116 of the second manifold 104of the first tube bank 100 and is distributed amongst a first portion ofthe heat exchange tube segments 106 to flow therethrough into the firstmanifold 102 of the tube bank 100. The refrigerant passes from the firstmanifold 102 into a second portion of the heat exchange tube segments106 and flows therethrough into an upper portion 118 of the secondmanifold 104 of the first tube bank 100 and is directed thereform backinto the refrigerant circuit of the refrigerant vapor compression system(not shown). Thus, the refrigerant circuit of the embodiment of themultiple bank heat exchanger depicted in FIG. 1 is a single pass-twopass, cross-counterflow refrigerant circuit.

Referring now to FIGS. 7-11, various other exemplary embodiments ofacceptable refrigerant circuit arrangements of the cross-counterflow,two tube bank heat exchanger 10 are illustrated schematically. In eachof FIGS. 7-10, the flow of air though the air side of the heat exchangeris in cross-counterflow as indicated by the arrow “A” and first throughthe first tube bank 100 and then through the second tube bank 200 asdiscussed previously with respect to FIG. 1. The flow of refrigerant,indicated by the arrow “R”, is first through the second tube bank 200and then through the first tube bank 100 in overall cross-counterflow tothe air passing through the air side of the heat exchanger 10. In theembodiment depicted in FIG. 7, the refrigerant flow circuit comprises asingle pass-single pass, cross-counterflow refrigerant circuit. In theembodiment depicted in FIG. 8, the refrigerant flow circuit comprises atwo pass-two pass cross-counterflow refrigerant circuit. In theembodiment depicted in FIG. 9, the refrigerant flow circuit comprises asingle pass-two pass variation of the single pass-two passcross-counterflow refrigerant circuit of FIG. 1. In the embodimentdepicted in FIG. 10, the refrigerant flow circuit comprises a twopass-three pass cross-counterflow refrigerant circuit.

Referring now to FIGS. 11 and 12, exemplary embodiments of acceptablerefrigerant circuit arrangements of the cross-counterflow, three tubebank heat exchanger 10 are illustrated schematically. In each of FIGS.11-12, the flow of air through the air side of the heat exchanger is incross-counterflow as indicated by the arrow “A” and first through thefirst tube bank 100, then through the second tube bank 200, and lastlythrough the third tube bank 300. The flow of refrigerant, indicated bythe arrow “R”, passes first through the third tube bank 300, thenthrough the second tube bank 200, and lastly through the first tube bank100 in overall counter flow to the air passing through the air side ofthe heat exchanger 10. In the embodiment depicted in FIG. 11, therefrigerant flow circuit comprises a single pass-single pass-single passcross-counterflow refrigerant circuit. In the embodiment depicted inFIG. 12, the refrigerant flow circuit comprises a single pass-twopass-three pass cross-counterflow refrigerant circuit.

Referring now to FIG. 13, there is depicted a multiple tube bankflattened tube heat exchanger 400 having three tube banks 100, 200, 300in a parallel-counterflow arrangement. In the embodiment depicted inFIG. 13, the flow of air through the air side of the heat exchanger, asindicated by the arrow “A”, passes first through the first tube bank100, then through the second tube bank 200, and lastly through the thirdtube bank 300. Each of the tube banks 100, 200, 300 comprises a two-passtube bank having a lower pass 130, 230, 330, respectively, and an upperpass 140, 240, 340, respectively. The flow of refrigerant, indicated bythe arrow “R”, is first generally parallel to the flow of air throughthe heat exchanger 400 and then generally counter to the flow of airthrough the heat exchanger 400. The refrigerant passes first through thelower pass 130 of the first tube bank 100, then through the lower pass230 of the second tube bank 200, then through the lower pass 330 of thethird tube bank 300, then through the upper pass 340 of the third tubebank 300, then through the upper pass 240 of the second tube bank 200,and lastly through the upper pass 140 of the first tube bank 100 andback into the refrigerant circuit (not shown). In the embodiment of theheat exchanger 400 depicted in FIG. 13, the number of heat exchange tubesegments varies progressively amongst the passes 130, 230, 330, 340,240, 140 with the least number of heat exchange tube segments being inthe lower pass 130 of the first tube bank 100, then increasingprogressively through the pass 230, 330, 340, 240 to the upper pass 140of the first tube bank 100 which has the greatest number of heatexchange tubes. Multiple bank flattened tube heat exchanger 400 isparticularly suitable for application as an evaporator in a refrigerantvapor compression system due to the progressively increasing refrigerantflow area provided as the refrigerant flows through the various passesof the of the three tube banks 100, 200, 300 in the progression ofpasses of increasing tube number as herein described as this arrangementaccommodates the change in density of the refrigerant as the refrigerantpasses through the evaporator. It has to be understood that in case therefrigerant condensation process is to take place inside the heatexchanger tubes, the number of tubes in each segment can progressivelydecrease.

With various well-optimized circuits, such as exemplified by therefrigerant circuits discussed herein, heat transfer performance wasimproved without noticeable penalty in the refrigerant side pressuredrop or fan power. The enhanced performance of the multiple tube bank,flattened tube finned heat exchanger 10 as disclosed herein permits coilvolume & face area of the heat exchanger to be reduced up to 25% ascompared to conventional single bank flattened tube heat exchangers.

Referring now to FIG. 14, there is depicted an exemplary embodiment of amultiple bank flattened tube folded fin plate heat exchanger 50 having afirst tube bank 510 having a plurality of multi-channel heat exchangetube segments 512 and a second tube bank 520 having a plurality ofmulti-channel tubes 522. The heat exchange tube segments 512 of thefirst tube bank 510 extend in parallel spaced relationship between afirst manifold (not shown) and a second manifold (not shown) as in themanner discussed earlier with respect to the first tube bank 100 of theheat exchanger 10. Similarly, the heat exchange tube segments 522 of thesecond tube bank 520 extend in parallel spaced relationship between afirst manifold (not shown) and a second manifold (not shown) as in themanner discussed earlier with respect to the second tube bank 200 of theheat exchanger 10. However, in the heat exchanger 50, the second tubebank 520 is arranged in spaced relationship at a relatively narrow gap,G, downstream with respect to airflow through the air side of the heatexchanger 50 of the first tube bank 510 with the heat exchange tubesegments 522 disposed in staggered relationship with the heat exchangetube segments 512 of the first tube bank 510.

Additionally, a first plurality of folded fin plates 530 is provided inthe first tube bank 510 with one folded fin plate 530 installed betweenand in heat transfer relationship with each pair of neighboring heatexchange tube segments 510 and a second plurality of folded fin plates540 is provided in the second tube bank 520 with one folded fin plate540 installed between and in heat transfer relationship with each pairof neighboring heat exchange tube segments 520. Each of the folded finplates 530, 540 comprises a continuous ribbon-like folded plate defininga plurality of fins 532, 542, respectively, that extended generallyorthogonal to the heat exchange tube segments 512, 522, respectively.Each of the fins may comprise a louvered fin. Each folded fin plate 530extends from the leading edge to the trailing edge of the heat exchangetube segments 512 of the first tube bank 510, but does not extend intothe second tube bank 520. Each folded fin plate 540 extends from theleading edge to the trailing edge of the heat exchange tube segments 522of the first tube bank 520, but does not extend into the first tube bank510. The terminology used herein is for the purpose of description, notlimitation. Specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as basis for teachingone skilled in the art to employ the present invention. Those skilled inthe art will also recognize the equivalents that may be substituted forelements described with reference to the exemplary embodiments disclosedherein without departing from the scope of the present invention.

While the present invention has been particularly shown and describedwith reference to the exemplary embodiments as illustrated in thedrawing, it will be recognized by those skilled in the art that variousmodifications may be made without departing from the spirit and scope ofthe invention. It is also to be understood that the heat exchangerdisclosed herein may be utilized in connection with refrigerant vaporcompression systems used in air conditioning, heat pump, andrefrigeration applications. Therefore, it is intended that the presentdisclosure not be limited to the particular embodiment(s) disclosed as,but that the disclosure will include all embodiments falling within thescope of the appended claims.

1-18. (canceled)
 19. A heat exchanger comprising: a first tube bankincluding at least a first and a second flattened tube segmentsextending longitudinally in spaced parallel relationship; a second tubebank including at least a first and a second flattened tube segmentsextending longitudinally in spaced parallel relationship, said secondtube bank disposed downstream with respect to airflow over said firsttube bank with a leading edge of the second tube bank spaced from atrailing edge of the first tube bank; and a continuous folded plate finextending between the first and second flattened tube segments of bothof said first tube bank and said second tube bank; wherein the air flowpasses first transversely across the flattened tube segments of saidfirst tube bank and then passes transversely across the flattened tubesegments of said second tube bank, and the refrigerant flows firstthrough the flattened heat exchange tube segments of said second tubebank and then through the flattened heat exchange tube segments of saidfirst tube bank.
 20. The heat exchanger as recited in claim 19 whereinsaid continuous folded plate fin comprises a louvered plate having afirst louvered section extending between the first and second flattenedtube segments of the first tube bank and a second louvered sectionextending between the first and second flattened tube segments of thesecond tube bank.
 21. The heat exchanger as recited in claim 20 whereinsaid continuous folded plate fin further comprises a transition sectionbetween the first louvered section and the second louvered section, thetransition section positioned between a trailing edge of said first tubebank and a leading edge of said second tube bank.
 22. The heat exchangeras recited in claim 21 wherein said transition section includescondensate drainage apertures.
 23. The heat exchanger as recited inclaim 21 wherein the first louvered section and second louvered sectionare symmetrical.
 24. The heat exchanger as recited in claim 21 whereinthe first louvered section and the second louvered section areasymmetrical.
 25. The heat exchanger as recited in claim 20 wherein thelouvers of the first louvered section are oriented at a forward angleand the louvers of the second louvered section are oriented at a backangle.
 26. The heat exchanger as recited in claim 19 wherein said firsttube bank and said second tube bank comprise tube banks having an equalnumber of flattened tube segments.
 27. The heat exchanger as recited inclaim 19 wherein one of said first tube bank and said second tube bankcomprises a tube bank having a lesser number of flattened tube segmentsthan the tube bank of the other of said first tube bank and said secondtube bank.
 28. The heat exchanger as recited in claim 19 wherein theflattened tube segments of said first tube bank have a first tube widthand the flattened tube segments of said second tube bank have a secondtube width being different from the first tube width.
 29. The heatexchanger as recited in claim 19 wherein each flattened tube segment ofsaid first tube bank comprises a multi-channel tube segment having afirst plurality of parallel flow channels and each flattened tubesegment of said second tube bank comprises a multi-channel tube segmenthaving a second plurality of parallel flow channels, the secondplurality of parallel flow channels being different in number from thefirst plurality of parallel flow channels.
 30. The heat exchanger asrecited in claim 19 wherein the heat exchange tube segments of saidsecond tube bank are arranged in a staggered arrangement with the heatexchange tube segments of said first tube bank.
 31. The heat exchangeras recited in claim 19 wherein: the refrigerant flows first through thefirst pass of the first tube bank, then through the first pass of thesecond tube bank, then through the second pass of the second tube bank,and then through the second pass of the first tube bank.
 32. The heatexchanger as recited in claim 31 wherein the first plurality of heatexchange tube segments of the first pass of the first tube bankcollectively define a first refrigerant flow area, the first pluralityof heat exchange tube segments of the first pass of the second tube bankcollectively define a second refrigerant flow area; the second pluralityof heat exchange tube segments of the second pass of the second tubebank collectively define a third refrigerant flow area, and the secondplurality of heat exchange tube segments of the second pass of the firsttube bank collectively define a fourth refrigerant flow area, therespective refrigerant flow areas becoming progressively larger from thefirst refrigerant flow area to the second refrigerant flow area to thethird refrigerant flow area to the fourth refrigerant flow area.